<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>vue</title>
    <script type="text/javascript" src="../../js/vue.js"></script>

</head>
<body>
    <div id="root">
        <h5>今天天气{{info}}</h5>
        <!-- <button @click="isHot = !isHot;x ++">切换天气</button> -->
        <button @click="changeWeather">切换天气</button>
    </div>

    <script type="text/javascript">
        Vue.config.performance = false;
        const vm = new Vue({
            el:'#root',
            data() {
                return {
                  isHot:true,
                };
            },
            computed:{
                info(){
                    return this.isHot ? '炎热' : '凉爽'
                }
            },
            methods: {
                changeWeather(){
                    this.isHot = !this.isHot
                }
            },
            watch:{
                // 正常写法 
                /* isHot:{
                    //immediate:true, // 初始化时调用
                    //deep:true,
                    // isHot 被修改时调用
                    // 只有handler时可以简写
                    handler(newValue,oldValue){
                        console.log("isHot 被修改",newValue,oldValue)
                        
                    }
                }, */
                // 简写
                /* isHot(newValue,oldValue){
                    console.log("isHot 被修改",newValue,oldValue)
                } */
            }
           
        })
        // 正常写法
        /* vm.$watch('isHot',{
            immediate:true, // 初始化时调用
            deep:true,
            handler(newValue,oldValue){
                console.log("isHot 被修改",newValue,oldValue)
            }
        }) */
        // 简写
        vm.$watch('isHot',function(newValue,oldValue){
            console.log("isHot 被修改",newValue,oldValue)
        })
      
    </script>

</body>
</html>